1. Field of the Invention
The invention relates to monitoring and controlling channels to improve the interface of calls, and more particularly to a method for monitoring B-channels for an ISDN basic rate line to improve the interface of video and voice calls.
2. Description of the Related Art
ISDN lines are becoming more common in single user environments (e.g., in single resident homes). Similarly, high speed data transmission, internet access, remote LAN access and video transmission is becoming more desirable. For example, telecommuters often use basic-rate interface ISDN lines to obtain high speed data transfer, internet access, remote LAN access and/or video transmission and reception. ISDN is an evolving set of standards for a digital network carrying both voice and data communications. Basic-rate interface ISDN lines are configured to include two bearer (or B) channels and one D-channel (commonly referred to as 2B+D). Each B-channel carries 64 kbps of digitized voice or data. Data is transferred on one or both of the bearer channels and information related to a call is transferred on the D-channel. Thus, the D-channel is the signaling channel. The D-channel carries 16 or 64 kbps, depending on the circuit type.
Currently, to participate in, for example, a high quality video conference, both of the B-channels in the ISDN line are used for data transmission. When this occurs, the voice device handler does not detect that both B-channels are in use. Therefore, if a voice call is received when both B-channels are in use, the switching unit (e.g., a central office or a PBX) attempts to connect the voice call to the user's voice terminal. In this situation, all the available B-channels are already in use, so the voice call cannot be connected. The telephone still rings when an incoming voice call is detected because the ring signal is sent on the available D-channel. As a result, if a user attempts to answer a ringing voice terminal under these circumstances, the user is presented with a dead telephone which is not connected to the incoming voice call.
FIG. 1 illustrates a prior art environment for utilization of an ISDN line. Private Branch Exchange (PBX) 100 is connected to ISDN line 102. Up to eight lines can be connected to this ISDN line, but only two lines can be used at one time because only two B-channels are available on an ISDN line. Video terminal 104 and telephone 106 are connected to PBX 100 via ISDN line 102. In the original configuration for an ISDN line, one voice terminal and one data terminal were envisioned. Each of these terminals were to use only one B-channel. Problems now arise because old software and new data terminals utilizing both B-channels provide high quality video transfer. In addition, problems arise when more than two devices are connected to one ISDN line because only two B-channels are available. When two B-channels are used, the device handler software does not detect the unavailability of the B-channels and attempts to connect a voice call to telephone 106 when both B-channels are used to provide data to video terminal 104. A ring signal is transferred on the D-channel. Therefore, in this example, telephone 106 rings as though a voice call is being provided at telephone 106. As stated above, in this situation, when the user attempts to answer telephone 106, no response is provided.
Similarly, if a user attempts to make a call on telephone 106 when both B-channels are being used to provide data to video terminal 104, the user would receive no response from telephone 106. No visual or audio indications are provided from the voice terminal when the B-channels are unavailable. Depending on the implementation of a particular voice terminal, a local busy tone may be provided on the telephone rather than a dead line. In both circumstances, telephone 106 rings as a result of an incoming call, but the B-channels are unavailable, so the call cannot be received.
Data devices are currently available to provide protection against B-channel contention. These devices simply drop one of the B-channels when a voice call arrives. This arrangement assumes that the user wants to receive the voice call. Additionally, when one of the B-channels is dropped, a degradation of the video display results because the data transmission for the video display is then provided on only one B-channel. To re-establish the full quality video, the user may have to place the video call again which incurs additional line charges. FIG. 2 illustrates an environment for a data device which provides protection against B-channel contention. These data devices are utilized in a central office switch environment. Typically, central office 120 is connected to data device/adapter 124 via ISDN line 122. Adapter 124 is either a card located in video terminal 126 or a separate box. Telephone 128 is directly connected to adapter 124. In this arrangement, when both B-channels are being used to provide a video display to video terminal 126, and an incoming voice call is detected by adapter 124, the user can pick up ringing telephone 128 and receive the voice call. This occurs because adapter 124 drops one of the B-channels and allows the voice call to be provided on that B-channel to telephone 128. In this arrangement, when the user picks up telephone 128, the video display being provided by video terminal 126 immediately degrades in quality.
It is desirable to have an adapter which does not automatically drop a channel and give priority to a voice call. It is also desirable to have a less expensive, configurable adapter which allows the user to determine how incoming calls will be handled when both B-channels are being used.